利用地面常规观测资料和NCEP/UCAR提供的逐日1°×1°间隔6 h FNL模式的全球对流层分析资料,对2019年5月11—12日发生在内蒙古西部地区的强沙尘暴事件进行等熵位涡分析。结果表明:沙尘暴发生时,从位温垂直剖面图上分析可以得到各等压面上位温垂直分布特征;在850~700 hPa上,等位温线近似垂直与横坐标,位温随着等压面升高而不变,低层大气十分接近绝热状态,混合层状态特征显著。在700~200 hPa上,取4个可以覆盖沙尘暴发生区域的位温垂直剖面图,位温取交集合并得位温取值范围;根据位温取值范围和相应的位势高度场,选取需要的位温,计算得到位势高度和位温所对应的等熵位涡;等熵位涡与位势高度场、全风速场、高空急流、西风低空急流、强沙尘暴发生区域之间存在着数值关系特征和位置关系特征。
We analyze the relationships between strato- spheric polar vortex anomalies and cooling events in eastern China using isentropic reanalysis data from the European Center for Medium-Range Weather Forecasts. Daily mean data from 2000 to 2011 are used to explore the effective stratospheric signals. First, diagnoses of the 2009/2010 winter show that after the stratospheric sudden warming （SSW） of the Atlantic-East Asian （AEA） pattern, the stratospheric high isentropic potential vorticity （IPV） center derived from the split polar vortex will move to the northeast of the Eurasian continent. The air mass, accom- panied by some southward and eastward movements and characterized by high IPV values, will be stretched verti- cally, leading to apparent reinforcements of the positive vorticity and the development of acold vortex system in the troposphere. The northerly wind on the western side of the cold vortex can transport cold air southward and down- ward, resulting in this distinct cooling process in eastern China. Secondly, the empirical orthogonal function ana- lyses of IPV anomalies on the 430 K isentropic surface during 2000-2011 winters indicate that the IPV distribution and time series of the first mode are able to represent the polar vortex variation features, which significantly influ- ence cold-air activity in eastern China, especially in the AEA-type SSW winter. When the time series increases significantly, the polar vortex will be split and the high-IPV center will move to the northeast of the Eurasian continent with downward and southward developments, inducing obvious cooling in eastern China. Moreover, all the four times SSW events of AEA pattern from 2000 to 2011 are reflected in the first time series, and after the strong polar vortex disturbances, cooling processes of different inten- sities are observed in eastern China. The cooling can sus- tain at least 1 week. For this reason, the first time series can be used as an available index of polar vortex oscillation and has the power to predict
